[cl-opengl-devel] Re: playing with opengl at the repl

[Jose A. Ortega Ruiz]

"Luís Oliveira" <luismbo at gmail.com> writes:

> On Sat, Jul 12, 2008 at 10:49 PM, Jose A. Ortega Ruiz <jao at gnu.org> wrote:
>
>> what would be the best way to have an OpenGL/GLUT window open and
>> manipulate it from a (non-blocked) REPL, maybe even while the GLUT main
>> loop is running.
>
> If you are using a multi-threaded Lisp, you can redefine e.g. your
> glut:display method and GLUT's main loop will pick it up. Otherwise,
> you'll have to interrupt the loop, redefine things, then resume it.
>

Yes, i'm using SBCL/Slime on Linux, and that seems to work so far. I
guess that the best way to interrupt the loop (as i've been suggested in
a private response) is to use restarts (one more thing for me to learn
properly): maybe providing some predefined restarts in cl-opengl itself
would be a good idea? (i could even try to send some patches, although
i've done very little serious CL programming so far).

> If you want to try GL commands at the REPL and watch their effect
> interactively then try something like this:
>
>     CL-USER> (let ((glut:*run-main-loop-after-display* nil))
>                (glut:display-window (make-instance 'glut:window)))
>     NIL
>     CL-USER> (progn
>                (gl:clear-color 1 0 0 0)
>                (gl:clear :color-buffer)
>                (gl:flush))
>

Hmm, maybe i'm missing something basic here, but that doesn't work. The
new window pops up, totally transparent, but the subsequent PROGN has no
effect: the window remains transparent.

> Running glut:main-loop in a separate thread seems to confuse GLUT, so
> when you need GLUT's help to handle some window event, you can call
> glut:main-loop-event which only handles at most one event per call,
> IIUC.
>

Yes, that seems to be the case. For instance, using a window instance
with dimensions other than the defaults needs a call to
glut:main-loop-event for the resizing to take effect. But then, as i
mentioned before, no drawing takes place.

Cheers,
jao
-- 
"Light thinks it travels faster than anything but it is wrong. No matter
 how fast light travels it finds the darkness has always got there first,
 and is waiting for it."
  -Terry Pratchett, Reaper Man